The determination of the direction and speed of a vehicle is of decisive importance in traffic monitoring and control for the detection of ghost drivers and compliance with speed restrictions. The determination of the distance between vehicles is used in tunnels, for example, to ensure that minimum distances are complied with to avoid rear end collisions.
A wide variety of systems are currently in use to determine the direction, speed and distance between vehicles, such as the use of light barriers, induction loops embedded into the roadway, radar or laser scanners etc. What all the known systems have in common is that they are extremely expensive. For example, induction loops require the surface of the roadway to be opened up, light barriers require installations on both edges of the roadway, and radar or laser scanners are structurally complex and costly and possibly emit undesirable disturbing electromagnetic radiation.